This application claims the priority of German Patent Application, Serial No. 101 59 893.9, filed Dec. 6, 2001, pursuant to 35 U.S.C. 119(a)-(d), the disclosure of which is incorporated herein by reference.
The present invention relates to a method for safeguarding an injection molding machine against a faulty operation.
Injection molding machines include at least two mold mounting plates, with one mold mounting plate fixedly anchored upon a machine bed and with the other mold mounting plate moveable relative thereto. The mold mounting plates carry respective half-molds which demarcate a cavity, when the half-molds are clamped together, to mold a plastic article. Opening and closing of the cavity involves a displacement of the moving mold mounting plate relative to the fixed mold mounting plate.
In the event an obstacle is encountered in its travel path, the movement of the moveable mold mounting plate may be inhibited and may lead to damage of the injection molding machine.
European Pat. No. EP 0 203 199 B1 describes a protection function which involves, on one hand, a reduction of the drive force for the moving mold mounting plate during travel, and, on the other hand, a check whether the mold mounting plate has traveled a predetermined distance. When the mold mounting plate has reached a first position, a time interval is measured. After elapse of this time interval, it is checked whether the mold mounting plate has reached a second position. If this is not the case, it is assumed that the mold mounting plate has hit an obstacle during its travel path so that the drive is deactivated and an alarm is triggered.
This conventional protection function suffers shortcomings because it is necessary to wait for the interval time to elapse so that blockage cannot immediately be recognized. As a consequence, it is conceivable that damage to the injection molding machine can occur during the initial interval time.
It would therefore be desirable and advantageous to provide an improved to obviate prior art shortcomings and to allow immediate detection of any blockage of a moveable component.
According to one aspect of the present invention, a method of safeguarding an injection molding machine against execution of a faulty operation, includes the steps of monitoring a movement state of a component of the injection molding machine as a drive for the component is activated, and deactivating the drive, when no movement or only a minimal movement of the component is detected.
The present invention resolves prior art problems by providing a safeguard function that allows immediate detection of a standstill in the absence of any change in position.
According to another feature of the present invention, the monitoring step may include a continuous monitoring of the speed of the component, wherein the drive is deactivated, when the speed reaches a predetermined minimum speed or approaches zero. Examples of suitable speed monitoring devices include sensors, such as induction sensors, moving coils, optical devices, or displacement pick-ups.
According to another feature of the present invention, the monitoring step may include a cyclical monitoring of a position of the component, wherein the drive is deactivated, when successive cycles establish no positional change or only a positional change below a predetermined minimum level. An example of a suitable monitoring device includes a displacement pick-up. When no change in position or only a minimal positional change of the component is registered, blockage is assumed and the drive is shut down.
According to another feature of the present invention, the monitoring step may include a position control system for continuously ascertaining an actual position value of the component as it moves, and comparing the actual position value with a desired position value from a displacement pick-up. During normal operation, the actual value trails the desired value within certain limits (lag error). When encountering an obstacle, the lag error increases, i.e. the difference between desired and actual values increases. Thus, the drive is deactivated, when the magnitude of a difference between actual position and desired position, i.e. the lag error, exceeds a predetermined value.
According to another feature of the present invention, a blockage may be detected also indirectly through provision of a drive control system for comparing cyclically a desired value of an operating parameter of the drive with a actual value of the operating parameter at any given time. Also in such a system, the actual value of a drive operating parameter trails the desired value, whereby in the event of a blockage, the difference between actual position and desired position exceeds a predetermined value, thereby deactivating the drive. A suitable operating parameter may be, e.g., the rotation speed of a motor, in particular an electromotor, whereby the rotation sensor is monitored.
Of course, the afore-stated measures may be combined by using a conventional displacement pick-up system for monitoring purposes and at the same time monitor the drive. The thus resultant redundancy is able to detect early on an error in the displacement pick-up system and/or in the drive monitoring system.
The method according to the present invention thus provides for immediate and direct error recognition and prevents therefore the need to wait for elapse of successive events (elapse of a monitoring time).
The method according to the present invention is applicable to monitor the movement of a moving mold mounting plate of an injection molding machine, e.g. electrically-operated as well as hydraulically-operated injection molding machines. Other examples of moving components that can be monitored include an ejection unit or an injection unit.
Implementation of the novel and inventive method according to the present invention may involve the use of sensors, e.g., a conventional measuring system, rotation sensor of a motor, additional speed sensors and the like, for generating signals that are transmitted to a controller for suitable processing in a manner as previously described for deactivating the drive and/or triggering of an alarm signal. The control unit may be a separate part or may be part of an already existing control system that has been suitably modified. Further details for implementation of a method according to the present invention are generally known to the artisan and thus are not described in detail for the sake of simplicity.
According to another aspect of the present invention, an injection molding machine, includes a fixed mold mounting plate; a moveable mold mounting plate; a drive for moving the moveable mounting plate relative to the fixed mold mounting plate; and a control system including a detector for monitoring a movement state of the moveable mold mounting plate during travel relative to the fixed mold mounting mold, and a controller operatively connected to the drive for deactivating the drive, when no movement or only a minimal movement of the moveable mold mounting plate is detected.